Extremely long term safe storage of nuclear wastes is a major problem for the nuclear industry and various proposals have been made for dealing with this problem. One proposal concerns immobilising the waste in a suitable borosilicate glass which can then be deposited in a suitable geological formation. However, doubts concerning possible devitrification of the glass and consequent leaching of radioactive elements have founded criticism of the safety of this technique.
Another recent proposal involves the formation of a synthetic rock in which the nuclear reactor waste is immobilised, details of this method being described by A. E. Ringwood et al in NATURE March 1979. According to the disclosed, a selected synthetic rock is formed with the radioactive elements in solid solution. The constituent minerals of the rock or close structural analogues have survived in a wide range of geochemical environments for millions of years and are considered highly resistant to leaching by water.
The nuclear reactor waste is incorporated into the crystal lattices of the synthetic rock in the form of a dilute solid solution and therefore should be safely immobilised. A dense, compact, mechanically strong block of the synthetic rock incorporating the nuclear waste is produced by pressure and heat in a densification process and the block may then be safely disposed of a suitable geological formation.
The following patent applications have been filed by the Australian National University based on the work by A. E. Ringwood et al:
U.S. patent application No. 54957 entitled "Safe Immobilisation of High Level Nuclear Reactor Wastes"; and
U.S. patent application No. 124953 entitled "A Process for the Treatment of High Level Nuclear Wastes".
The present application, in some embodiments, is concerned with making use of the synthetic rock arrangements of A. E. Ringwood et al and is concerned with an apparatus and method for producing disposable blocks of materials which can include radioactive wastes in an immobilised form. However, the present application is not necessarily restricted to the particular classes of synthetic rocks of A. E. Ringwood et al and the apparatus and method described herein could be applied to other synthetic rocks in addition to those specifically described by A. E. Ringwood et al.
Other examples of synthetic rock systems which might be used with aspects of the present invention could include the following:
1. Supercalcine (G. J. McCarthy, Nuclear Technology, Vol. 32, January 1977) PA0 2. Product of Zeolite Solidification Process (IAEA Technical Report Series No. 176, pages 51). PA0 3. Product of Titanate Solification Process (IAEA Technical Report Series No. 176, pages 53). PA0 4. Product of the Sandia Process (R. W. Lynch and R. G. Dosch, US Report SAND-75-0255 (1975). PA0 (a) establishing a quantity of supply material in a cylindrical container, means being provided by preventing gross outward deformation of the cylindrical container during the method, the cylindrical container being sufficiently heat and corrosion resistant to contain the supply material during and after the method has been effected and the supply material comprising material for forming the synthetic rock and a minor proportion of nucler reactor waste capable of being immobilised in the synthetic rock when densified into a block; PA0 (b) applying pressure to compress the supply material along an axis of the container and applying heat to cause densification and the formation of a block of synthetic rock including the nuclear reactor waste; and PA0 (c) either before or after said densification step, sealing the container with a metal cap whereby the sealed container is adapted to be removed and placed in a suitable long term storage location.
For the purposes of this specification, synthetic rock is defined as a material which consists chemically of one or more metal oxides (or compounds derived from metal oxides which have been formed into a rock-like structure) by subjecting a mass of solid particles of the material to heat and pressure.